The use of fasteners employing hydraulically operated components to apply bolt tension is well established. Examples can be found in U.S. Pat. No. 5,730,569 (Bucknell) (=International Application PCT/AU93/00477=International Publication WO 94/07042). Such fasteners are intended to be installed in a manner allowing their periodic removal for servicing or for maintenance of the equipment on which they are fixed. They are seldom used in situations where they may be permanently applied. Factors which discourage the latter are high initial cost compared to other methods of permanent fixing and deterioration of hydraulic seal material over time especially at elevated temperatures.
U.S. Pat. No. 5,730,569 discloses hydraulic fasteners which are simple and therefore inexpensive to produce. However the latter rely on the preservation of seal integrity to maintain the tensile layers in the bolts on which they are applied. Because of the above factors, hydraulically assisted fasteners have not been used in the construction of undersea pipelines nor of conduits for the fixing of flange joins on pipelines, valves and the like. Current methods require divers to operate multiples of specially constructed hydraulic bolt tensioners simultaneously to close underwater flange joints. The cost of such operations is high since they require an entire diving support vessel and crew, as well as divers.
Also the risk to personnel and equipment increases significantly with greater depth as well as the cost. As shallower fields are depleted in offshore oil and gas exploration, drilling and production move to deeper waters, and these factors become significant in determining viability. Remote Operated Vehicles (ROVs) are used to perform complex bolting operations at depth where divers' time is severely restricted. These vehicles are limited in their dexterity and even more unreliable in delivering a satisfactory outcome when encumbered by lack of visibility or limited mobility. Currents and other local environmental conditions can also affect operations and cause a blow out in operating expenses.
It is an object of the present invention to provide hydraulically assisted fasteners and hydraulic tensioning devices which operate without hydraulic seals to directly tension bolts or members on which they are applied or at least provide a useful alternative to the prior art devices.
It is a further object to provide fasteners and devices which do not require locking rings to secure the tensile load produced and which are not subject to the degradation of seal material and which may be used with a charging medium which will not degrade under prevailing operating conditions.